1. Field of the Invention
The invention relates to a lead frame for light-emitting diode (LED), particularly a dual layered lead frame structure for the flip chip packaging process of LED.
2. Description of Related Art
The conventional flip chip packaging of a high-power LED has been primarily known to use ceramic substrates. The ceramic substrates contain ceramic base material and conductive pattern. The conventional ceramic base material is a single layer one containing conductive through holes. The surface of the ceramic base material is covered with copper foil and heated afterward at a high temperatures (1065˜1085° C.) to cause copper foil and the ceramic base material being eutectic together. The high temperature melt copper foil will be filled in the through holes forming conductive leads. The electric circuitry of the LED will be formed on the ceramic substrate by etching process. The ceramic base material substrate is made from aluminum nitride or aluminum oxide formed by burning at a high temperatures (850˜900° C.).
As shown in FIG. 1 which is a sectional view of a conventional lead frame, the ceramic substrate 2 is constructed with a die bonding unit 21 which supports the LED chip 3, a ceramic base material 20 and a solder unit 22. The ceramic base material 20 is made of aluminum nitride or aluminum oxide and the ceramic base material 20 form with a conductive body hole 200. The ceramic base material 20 is formed by using a high temperature burning process. The ceramic base material 20 is made of aluminum nitride or aluminum oxide mixed with glass material and the cohesive agent uniformly to become pulpy slurries. It is then formed into a sheet to be heated. The entire ceramic substrate 2 is also formed by using a high temperature heating process to eutectic copper foil to the ceramic base material 20. It is understood that the cost of manufacturing the ceramic substrate 2 is higher than the same for manufacturing a lead frame. Also, the ceramic substrate 2 may easily be damaged to break, and has low mechanical durability. The heat dissipation of the ceramic substrate 2 is mainly through the ceramic substrate material. The coefficient of thermal conductivity of ceramic base material 20 made of aluminum nitride is about 170˜230 W/Mk. The coefficient of thermal conductivity of ceramic base material 20 made of aluminum oxide is about 20˜24 W/mK. Comparatively, the coefficient of thermal conductivity of copper used in the lead frame is about 398 W/mK. Therefore, the thermal conductivity efficiency of the ceramic base material 20 is much lower than the same of the lead frame.
Notwithstanding the prior art, the invention is neither taught nor rendered obvious thereby.